A semiconductor device, such as a switching device or a diode, is used in a circuit such as a switching power supply or an inverter. The semiconductor device requires a high breakdown voltage and low on-resistance. The relationship between the breakdown voltage and the on-resistance is a trade-off relationship which is determined by semiconductor material used for the semiconductor device.
With the progress of technical development, the on-resistance of semiconductor device is reduced to the limit of silicon which is a major semiconductor material. It is necessary to change the semiconductor material in order to further improve the breakdown voltage or to further reduce the on-resistance.
A GaN-based semiconductor, such as gallium nitride (GaN) or aluminum gallium nitride (AlGaN), has a wider bandgap than silicon. When the GaN-based semiconductor is used for switching device, it is possible to improve the trade-off relationship determined by the semiconductor material and to significantly increase the breakdown voltage or to significantly reduce the on-resistance.
However, for example, a switching device using the GaN-based semiconductor has the problem of “current collapse” in which, when a high drain voltage is applied, on-resistance increases.